1. Field of the Invention
The invention relates to a method and apparatus for fabricating a phase-change recording medium. In particular, the invention relates to a method and apparatus for fabricating a phase-change recording medium, capable of initial crystallization to the phase-change recording media.
2. Description of the Related Art
In recent phase-change recording media including such recording media as phase-change optical disks and optical memory cards, data record and reproduction are performed by utilizing the characteristic that when a phase-change recording layer formed on the substrate is irradiated with a laser beam, the irradiated portion of the phase-change recording layer varies in reflectivity depending on whether the portion is crystal or amorphous.
The recording layers of the phase-change recording media are formed by vacuum evaporation and sputtering technologies. The formed recording layers usually have a surface of low reflectivity, and tend to make the automatic focusing and tracking of a beam spot unstable. Accordingly, the phase-change recording media fabricated require initial crystallization over the entire recording layers in advance of users"" use.
The initialization apparatus for performing the initial crystallization of a phase-change type optical disk according to the conventional art comprises: a high power semi-conductor laser; a collimating lens for polarizing a diffused light beam radiated from the semi-conductor laser into a parallel beam; and an objective lens for focussing the parallel beam output from the collimating lens into a light spot on the recording layer of the recording medium. Here, the light beam output from the high power semi-conductor laser is formed into the light spot through the collimating and objective lenses so that the light spot heats the recording layer up to a temperature in the range of its crystallizing and melting points for initial crystallization. This initial crystallization consumes approximately 20-60 seconds for each phase-change type optical disk.
In the above-described initial crystallization technology in the conventional art, phase-change type optical disks were fabricated before loaded into the initialization apparatus one by one, each consuming an initial crystallization time of approximately 20-60 seconds. This complicated the initial crystallization operation and made the processing time lengthy as well, ending up with a problem of increased costs of the phase-change type optical disks.
The documents describing the above-mentioned technology of applying initial crystallization to a phase-change type optical disk include Japanese Patent Laid-Open Publication No. Hei 5-342629, Japanese Patent Laid-Open Publication No. Hei 11-3522, Japanese Patent Laid-Open Publication No. Hei 10-198959, Japanese Patent Laid-Open Publication No. Hei 10-172145, Japanese Patent Laid-Open Publication No. Hei 09-293247, Japanese Patent Laid-Open Publication No. Hei 09-161316, Japanese Patent Laid-Open Publication No. Hei 07-334845, Japanese Patent Laid-Open Publication No. Hei 07-272272, and Japanese Patent Laid-Open Publication No. Hei 06-012670.
An object of the present invention is to provide a method and apparatus for fabricating a phase-change recording medium, which eliminate the need for initial crystallization operations by dedicated initialization apparatuses. Specifically, the present invention has the following objects:
A first object of the present invention is to provide a method and apparatus for fabricating a phase-change recording medium in which the fabrication and initial crystallization of a phase-change recording medium can be performed at the same time.
A second object of the present invention is to provide a method and apparatus for fabricating a phase-change recording medium in which the fabrication and initial crystallization of a phase-change recording medium can be performed, with the initial crystallization at high speed.
In addition to the second object, a third object of the present invention is to provide an easy-to-design method and apparatus for fabricating a phase-change recording medium.
To achieve the foregoing objects, the present invention provides a method for fabricating a phase-change recording medium for depositing particles of phase-change recording material onto a substrate to form a coat of phase-change recording layer, the method comprising: a first step of loading a substrate, especially a disk-like substrate into a vacuum chamber; a second step of filling the vacuum chamber with sputtering gas; an optional third step of rotating the substrate; a fourth step of depositing sputtering particles struck out of a sputtering target onto the substrate to form a phase-change recording layer; and a fifth step in which when the sputtering particles are deposited on the substrate up to a predetermined thickness in the fourth step, a crystallization energy supply mechanism irradiates the sputtering-particle-deposited substrate with a laser beam having energy necessary for initial crystallization. This makes it possible to perform the fabrication and initial crystallization of a phase-change recording medium at the same time. As the crystallization is made directly on the recording layer (without additional covering layers) and under vacuum , crystallization times and energy, may be reduced.
Moreover, the method for fabricating a phase-change recording medium according to the present invention may include a fifth step in which a crystallization energy supply mechanism irradiates the phase-change recording layer just formed in the fourth step with a laser beam having energy necessary for initial crystallization. This makes it possible to perform the fabrication and initial crystallization of a phase-change recording medium, with the initial crystallization at high speed.
Besides, an apparatus for fabricating a phase-change recording medium according to the present invention comprises: optionally a rotating mechanism for bearing and rotating a phase-change recording medium; a sputtering target made of a GeAsTe- or AgInAsTs-type alloy or the like; a cathode for striking sputtering particles of the GeAsTe- or AgInAsTs-type alloy or the like out of the sputtering target and depositing the sputtering particles struck out of the sputtering target onto a substrate to form a phase-change recording layer; and a crystallization energy supply mechanism for irradiating the sputtering-particle-deposited substrate with a laser beam having energy necessary for initial crystallization when the sputtering particles are deposited up to a predetermined thickness on the substrate. This makes it possible to perform the fabrication and initial crystallization of a phase-change recording medium at the same time.
The apparatus for fabricating a phase-change recording medium according to the present invention may also comprise a target fabrication chamber, an initial crystallization chamber, and a transporting mechanism. The target fabrication chamber includes a sputtering target and a cathode for depositing sputtering particles struck out of the sputtering target onto a substrate to form a phase-change recording layer. The initial crystallization chamber may include a rotating mechanism for bearing and rotating a phase-change recording medium, and a crystallization energy supply mechanism for irradiating the phase-change recording layer of a transported phase-change recording medium with a laser beam having energy necessary for initial crystallization. The transporting mechanism transports a phase-change recording medium having a just-formed phase-change recording layer, from the vacuum chamber to the initial crystallization chamber. The initial crystallization chambers is also put under vacuum. Transport between the target fabrication chamber and the crystallization chamber is also made under vacuum. This makes it possible to perform the fabrication and initial crystallization of a phase-change recording medium, with the initial crystallization at high speed. As the crystallization is made under vacuum and directly on the sputtered particles, crystallization energy may be reduced and crystallization times may be shortened.
Furthermore, in the apparatus for fabricating a phase-change recording medium according to the present invention, the crystallization energy supply mechanism may irradiate the recording layer with a single laser beam formed by an array of lasers extending in a radial direction of the phase-change recording medium, to apply the initial crystallization to the recording area of the recording layer. Alternatively, the crystallization energy supply mechanism may irradiate the recording layer with a plurality of laser beams to apply the initial crystallization to the recording area of the recording layer, the laser beams extending in radial directions of the phase-change recording medium and being separated from each other in the circumferential direction of the same. This allows a phase-change recording medium to be fabricated and subjected to initial crystallization. The use of on array of lasers or of a plurality of lasers also allows to shorten the crystallization time, because larger surface areas may be treated at the same time. If the width of the laser beam is as large as about half the diameter of a disk-like substrate, crystallization may be made within one revolution of the disc. It is, however, also possible to use one single laser beam which scans the surface of the disc.
The inventions is especially suitable for forming optical recording media such as compact discs or digital versatile discs. Such discs typically are formed as a plurality of layers. On a first dielectric layer there is arranged a protective layer followed by a recording layer. The recording layer is covered with an optional interface or protection layer, followed by a second dialectricum and an optical reflecting layer formed of metal material. The recording layer is amorphous when formed and is crystallized according to the present invention.
Instead of an optical disc having one single recording layer discs with a plurality of recording layers may be formed according to the present invention. In such a case, the above mentioned layer construction is repeated a number of times. Instead of an optical reflecting layer, partially reflecting layers are used in such a case. The present invention allows to crystallize each recording layer separately, before subsequent layers are formed. The present invention therefore allows to crystallize each recording layer in a precise and defined manner. The energy for crystallization and the time necessary for crystallization can be reduced therewith.
The method and the apparatus according to the present invention may also be used for producing other recording media than optical discs, such as hard-discs, where thin film layers have to be initialized by means of energy supply mechanisms in the form of lasers. The invention may also be used in the field of nano-technology.
It is also conceivable to directly irradiate sputtering particles struck out of the sputtering target so that the particles themselves are provided with energy necessary for initial crystallization.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.